Solid Particle Erosion Behavior of La2Ce2O7/YSZ Double-Ceramic-Layer and Traditional YSZ Thermal Barrier Coatings at High Temperature
, Gang Yan 2, Qianwen Wang 2, Li Yang 2,3,* and Yichun Zhou 2,3,*Round 1
Reviewer 1 Report
1. choosing the thickness of BC and TC is to be justified. and Thermal barrier coatings (TBC) on the turbine blade surface were considered the most effective method to greatly improve the operating temperature- wisely referred to this article will be useful in high temperature. https://doi.org/10.4028/www.scientific.net/AMM.787.912
2. solid version of a blade with different conditions and environments has to be documented in the intro section.
3. emissivity of the sample was determined as 0.88 by calibration test has to be checked with the literature and was thought to be high. Please check this result.
4. after 360 cycles, edge failure was a major finding in the eroded sample, not elaborately documented in the results and discussion section.
5.Figure 10. spalling of TBC was found but in the intro section, erosion of the study of TBC and associated mechanisms were not elaborated.
6.Figure 14, transverse cracks in TBC revealed the chosen parameter of the coating was still adjusted to meet the service requirements.
Author Response
Response:
We sincerely thank the reviewer for thoroughly examining our manuscript and providing very helpful comments to guide our revision. We have tried our best to revise all the comments and suggestions and we have provided a point-by-point response to the reviewers’ comments below:
Response 1: We are very appreciative of the suggestions. We have added the explanation of the thickness design of the BC and TC layers in Section 2.1: “The thickness of BC layer and TC layer are typical values in the TBC system. BC layer with this thickness improves the oxidation resistance of the substrate and the adhesion property between the TC layer and the substrate. TC layer with this thickness provides the thermal insulation.”
We thank the reviewer for recommending this valuable paper and we have cited it in the Introduction part.
Response 2: We sincerely thank the reviewer for the advice. We have revised the contents in the Introduction section: “NiCoCrAlY BC layer and Y2O3 stabilized ZrO2 (YSZ) TC layer were deposited on the circular sheets and model turbine blades. The SPE failure behavior of TBC-coated circular sheets and blades was studied under 1100 °C at the erosion angles of 60° and 90°.”
Response 3: We sincerely appreciate the reviewer for this comment. We have checked the emissivity of YSZ coating in other researchers’ work, and the result shows the value 0.88 used in the current paper is not high. In the work of Hu [1], the emissivity of YSZ at 1100 °C is up to 0.978. It is worth mentioning that the emissivity depends on the wavelength of infrared thermometer and the emissivity can reach to 0.98 when using long wavelength infrared [2].
Response 4: We sincerely thank the reviewer for this comment. We have revised the discussion part in section 3.1.4 to emphasize the importance of the edge failure: “There is no doubt that the spallation of TBC at the edge regions of the circular sheets is the most crucial reason for the TBC failure under thermal shock tests and SPE.”
Response 5: We sincerely appreciate the reviewer for this comment. In this paper, the spallation of coating on the edge region of the circular sheets was observed not only after SPE test (Fig. 9 and Fig. 10) but also after the thermal shock test (Fig. 11 and Fig. 12). We suggest the main reason for the edge failure of the surface TBC should be attributed to the stress concentration at the edge region when suffering the thermal stress during the thermal shock. Therefore, to be more precisely, edge failure cannot be considered as one of the erosion mechanisms.
Moreover, as discussed in section 3.1.4, there are total three types of erosion failure mechanisms of TBC according to other researchers’ work: type I, mild erosion by near-surface cracking; type II, compaction damage mode that a dense zone forms under the particle impacts; type III, severe erosion by foreign object damage and large-scale plastic deformation occurs.
Response 6: We thank the reviewer for this valuable comment. The formation of transverse cracks at the TC/BC interface due to the growth of TGO layer is a typical failure mode during the exposure of TBC at high-temperature atmospheres. The main reason for the growth of TGO is that the oxidation of the MCrAlY. Therefore, we will further improve oxidation resistance of the MCrAlY BC layer by adjusting the elemental contests and the coating deposition technique in the further. This is also a very popular topic in the field of TBC.
Reference:
[1]. Hu, X., et al., Failure Mechanism of EB-PVD Thermal Barrier Coatings under the Synergistic Effect of Thermal Shock and CMAS Corrosion. Coatings, 2022. 12(9): p. 1290.
[2]. Manara, J., et al., Long wavelength infrared radiation thermometry for non-contact temperature measurements in gas turbines. Infrared Physics & Technology, 2017. 80: p. 120-130.
Reviewer 2 Report
The introduction must be improved. The importance of TB must be proven by specifying the usage areas. As an example, by referring to the articles mentioned below, the following articles can be added to the study to show that the coatings are used in different fields of study areas.
1. https://doi.org/10.3390/coatings11070792
2. https://doi.org/10.3390/coatings12050690
3. https://doi.org/10.3390/coatings12101561
4. https://doi.org/10.3390/coatings12101552
The type of paper should be selected at the beginning of the first page of the article.
Why LCO-YSZ TBC was chosen. It must be explained.
The long form La2Ce2O7 must be written.
Line 56 requires the long spelling of EB-PVD.
On page 13, thermal conductivity and expansion coefficients are mentioned in the last paragraph. These values must be given. It can be given as a table.
It is not specified whether the article was funded elsewhere.
Author Response
Response:
We sincerely thank the reviewer for thoroughly examining our manuscript and providing very helpful comments to guide our revision. We have tried our best to revise all the comments and suggestions and we have provided a point-by-point response to the reviewers’ comments below:
Response 1: We thank the reviewer for this valuable suggestion and we appreciate the reviewer for recommending these valuable papers. We have improved the Introduction section by citing the recommended papers.
Response 2: We sincerely appreciate the reviewer for this comment. The type of the paper has been selected as Article at the beginning of the first page of the article.
Response 3: We sincerely thank the reviewer for this comment. We have added the reason for choosing LCO-YSZ as TBC in the Introduction part: “The development of A2B2O7 compounds especially La2Ce2O7 is a hot topic in the research field of TBC due to its high melting point, high-temperature phase stability, and excellent chemical corrosion resistance. But the thermal cycle life of single layer LCO TBCs is short and the coating is extremely easy to flake off due to its low fracture toughness. The design of La2Ce2O7-YSZ double layer TBC can effectively solve this problem.”
Response 4: We thank the reviewer for this valuable suggestion. We have revised all “LCO” to long form “La2Ce2O7” in the whole manuscript.
Response 5: We thank the reviewer for pointing this mistake out. Long spelling of EB-PVD has been added in line 56.
Response 6: We thank the reviewer for this valuable suggestion. We have added the thermal expansion coefficient data in the last graph of the page 13: “Firstly, the thermal expansion coefficient (CTE) of La2Ce2O7 (11.21×10-6 K-1) is higher than YSZ (11.08×10-6 K-1) at 1100 °C, and its CTE is close to the MCrAlY BC layer (13-15×10-6 K-1)”
Response 7: We thank the reviewer for raising this question. The funds of this paper were listed in the Acknowledgment section.
Reviewer 3 Report
This paper is interesting, well-explained and well-suited for the Thermal Barrier Coatings Structures, Properties, and Application special issue of this Journal.
However, there are only twelve References given in the Reference section but the authors have cited a total of [36] References. Please add the missing References [13-36]. This is mandatorily required.
In Fig. [13] please use the same magnification and same scale bar in all micrographs.
Please explain Figures [3-5] in little detail, especially about the necessity to add these Figures to this manuscript.
Author Response
Response:
We sincerely thank the reviewer for thoroughly examining our manuscript and providing very helpful comments to guide our revision. We have tried our best to revise all the comments and suggestions and we have provided a point-by-point response to the reviewers’ comments below:
Response 1: We thank the reviewer for pointing this mistake out. We have revised the reference part in the new version of the manuscript.
Response 2: We sincerely appreciate the reviewer for this valuable suggestion. However, in Fig. 13, the purpose of the Fig. 13(a) is to show the grains of YSZ coating. If we use an image with lower magnification, details about the YSZ grains cannot be displayed clearly. It’s the reason why we use the image with higher magnification. However, in Fig. 13(b)-(d) after tests, the surface of the YSZ has been severely destroyed and the grains of YSZ cannot be clearly identified, so it doesn’t make sense to use image with high-resolution. Moreover, the four images in Fig. 13(b)-(d) are in same magnification. In conclusion, we think Fig. 13 in the manuscript is the best way to display the results before and after tests.
Response 3: We sincerely thank the reviewer for this valuable comment. We have deleted the Fig. 4-6 in the manuscript because we think it is too redundancy to display these experimental procedures. Besides, we think Fig. 3 is important and we have added explanations about Fig. 3 in the revised manuscript.
Round 2
Reviewer 1 Report
The author addressed all issues.
Reviewer 2 Report
The study is valuable because it contributes to the literature.
Reviewer 3 Report
I am satisfied with the response of the authors and with a revised version of the manuscript.
